1. Field of the Invention
The invention relates to a coaxial probe scanning a surface of an object with a probe to thereby monitor a physical quantity such as a shape of the surface or an electrical characteristic of the object. The invention further relates to a scanning micro-wave microscope including the above-mentioned coaxial probe for forming an image of a surface of an object.
2. Description of the Related Art
A scanning probe microscope has a resolution in atomic level, specifically, a resolution of an order of nanometer or smaller. In addition, a scanning probe microscope has a function of forming an image of a three-dimensional shape, based on information including a profile of height of an object. Hence, a scanning probe microscope is used in many fields.
It is assumed that a coaxial cable defining a coaxial resonator to be excited by micro-waves is formed at an end surface thereof with an opening. If the opening of the coaxial cable is made to approach a surface of an object, an impedance or electric coupling of the opening is varied, and accordingly, a resonance frequency of the coaxial resonator is shifted, and a Q-value of the coaxial resonator is also varied.
Accordingly, as a surface of an object is scanned with the opening of the coaxial cable, a resonance frequency or Q-value of the coaxial cable is varied. As a result, it would be possible to form an image of a surface of an object, based on variation of the resonance frequency or Q-value.
A scanning micro-wave microscope operates under the above-mentioned principle. For instance, an example of a scanning micro-wave microscope is suggested in Applied Physics Letters, Vol. 72, pp. 1778-1780,1989.
In operation of the suggested scanning micro-wave microscope, an opening of a coaxial cable is positioned slightly above a surface of an electrically conductive object, the surface is scanned with the opening of the coaxial cable, it is detected what degree a frequency is shifted in dependence on a distance between the opening of the coaxial cable and the surface of the object, and an image of the surface of the object is formed based on the detected degree.
A scanning micro-wave microscope has an image resolution of {fraction (1/1000)} of a wavelength of a micro-wave or smaller, which means that the scanning micro-wave microscope constitutes a so-called proximity field microscope.
In particular, a point at which a resonance frequency is shifted and/or a Q-value is varied, detected by a scanning micro-wave microscope, corresponds to a point at which conservation energy and/or dissipation energy of a system defined by an object and a coaxial resonator are(is) varied.
A scanning micro-wave microscope is required to have a resolution which is generally equal to xc2xd to xc2xc of a diameter detected by a tip end of an electrical conductor extending through a coaxial cable. In order for a scanning micro-wave microscope to have such a resolution, it would be necessary for the electrical conductor to approach a surface of an object at a distance of a diameter of the tip end of the electrical conductor or smaller.
However, in the above-mentioned conventional scanning micro-wave microscope, since the electrical conductor of the coaxial cable is made directly to approach a surface of an object, a closest distance between the electrical conductor and a surface of an object could be just few micrometers. If the electrical conductor is positioned relative to a surface of an object at a distance smaller than the above-mentioned closest distance, just a few micrometers, the electrical conductor might collide with a surface of an object or make uncontrollable contact with a surface of an object. This means that a scanning micro-wave microscope or a proximity field microscope cannot accomplish its best performance, because it works better when it is located at a smaller distance from a surface of an object.
Japanese Unexamined Patent Publication No. 8-248322 has suggested an attachment module for measuring a focus of an objective lens, including a plate, a support mounted on the plate, a positioning device for positioning an object relative to the support in two directions perpendicular to each other, and a probe having a tip end, composed of glass fibers and mounted on the positioning device.
Japanese Unexamined Patent Publication No. 9-178760 has suggested a scanning probe microscope including a cantilever, a probe mounted on a tip end of the cantilever, a detector for detecting a physical quantity appearing between the probe and the object, a mover for three-dimensionally moving the probe and the object, a controller for controlling an operation of the mover, and means for moving the scanning probe microscope.
However, the above-mentioned problems remain unsolved even in the scanning probe microscopes suggested in the above-mentioned Publications.
In view of the above-mentioned problems in the conventional scanning probe microscope, it is an object of the present invention to provide a coaxial probe which is capable of making a probe approach a surface of an object at a distance of a diameter of an electrical conductor extending through a coaxial cable or smaller to thereby measure an impedance along a surface of an object.
It is also an object of the present invention to provide a scanning probe microscope including such a coaxial probe.
In one aspect of the present invention, there is provided a coaxial probe including (a) a coaxial cable including an electrical conductor extending therethrough and projecting therefrom at an end thereof, (b) a planar waveguide on which the electrical conductor projecting from the coaxial cable is mounted, and (c) a sensor electrically connected to the electrical conductor through the planar waveguide.
For instance, the planar waveguide may be comprised of (b1) a substrate, and (b2) a strip line formed on the substrate, the strip line being electrically connected at one end to the sensor and at the other end to the electrical conductor.
For instance, the planar waveguide may be comprised of (b1) a substrate, and (b2) a coplanar line formed on the substrate, the coplanar line being electrically connected at one end to the sensor and at the other end to the electrical conductor.
For instance, the sensor may be comprised of (c1) a cantilever supported at a distal end thereof on the planar waveguide, and (c2) a probe mounted on a free end of the cantilever.
It is preferable that the coaxial probe further includes a support which fixes the cantilever at the distal end of the cantilever onto the planar waveguide.
It is preferable that the support and the cantilever are located on an extension of the electrical conductor and are inclined relative to an axis of the electrical conductor.
It is preferable that the sensor is excited at a frequency close to a resonance frequency of a movement of the cantilever.
It is preferable that the sensor is detachable from the coaxial cable or from the coaxial cable.
There is further provided a coaxial probe including (a) a coaxial cable including a first electrical conductor extending therethrough, (b) a first connector non-separatable from the coaxial cable, (c) a second connector detachably coupled to the first connector and including a second electrical conductor extending therethrough and projecting therefrom at an end thereof, the second electrical conductor being electrically connected to the first electrical conductor when the first and second connectors are coupled to each other, (d) a planar waveguide on which the second electrical conductor projecting from the second connector is mounted, and (e) a sensor electrically connected to the second electrical conductor through the planar waveguide.
There is still further provided a coaxial probe including (a) a coaxial cable including an electrical conductor extending therethrough and projecting therefrom at an end thereof, (b) a planar waveguide on which the electrical conductor projecting from the coaxial cable is mounted, (c) a sensor electrically connected to the electrical conductor through the planar waveguide, (d) an electrically insulating sensor holder making contact with the sensor, and (e) a device for compressing the sensor holder onto the sensor.
For instance, the device may be comprised of a screw. As an alternative, the device may be comprised of a lever supported for rotation, and an actuator which actuates the lever such that the lever compresses the sensor holder onto the sensor.
There is yet further provided a coaxial probe including (a) a coaxial cable including an electrical conductor extending therethrough and projecting therefrom at an end thereof, (b) a planar waveguide on which the electrical conductor projecting from the coaxial cable is mounted, (c) a sensor electrically connected to the electrical conductor through the planar waveguide, (d) a sensor holder making contact with the sensor, (e) a device for compressing the sensor holder onto the sensor, (f) a piezoelectric device incorporated in the sensor holder, and (g) an electrode terminal extending from the piezoelectric device outwardly of the coaxial cable.
There is still yet further provided a coaxial probe including a coaxial cable including an electrical conductor extending therethrough and projecting therefrom at an end thereof, the electrical conductor including a bending portion and a sharpened tip end, the bending portion defining a cantilever and the sharpened tip end defining a probe.
In another aspect of the present invention, there is provided a scanning micro-wave microscope including (a) one of the above-mentioned coaxial probes, and (b) a controller. The sensor includes a cantilever supported at a distal end thereof on the planar waveguide, and a probe mounted on a free end of the cantilever. The controller controls a distance between the probe and an object, based on a detection signal indicative of displacement of a free end of the cantilever, and scanning a surface of the object with the probe to thereby form an image of the surface of the object.
The advantages obtained by the aforementioned present invention will be described hereinbelow.
In accordance with the present invention, it would be possible to make the coaxial probe approach a surface of an object at a distance which is a general level in an interatomic-force microscope, and measure an electric capacity along irregularities of a surface of an object.
In addition, since it would be possible to exchange a sensor to be used in an interatomic-force microscope, into another one, a coaxial probe suitable for measurement could be selected.
The above and other objects and advantageous features of the present invention will be made apparent from the following description made with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the drawings.